As a vehicle is operated on a road, irregularities in the road surface induce movements of the vehicle's tires. These movements in turn are transmitted through the vehicle suspension to the vehicle interior. In some instances, these movements may be transferred from the road to the steering wheel, and may be discernable by the driver as unwanted vibrations.
In addition, there may be irregularities in rotating components located at corners of vehicles, such as imbalance, out of roundness and eccentricities in tires, wheels and brake rotors. These irregularities may also result in internal vehicular forces which produce movements that are transmitted to the vehicle interior. These movements are most notable on smooth roads as vibrations in proximity of the occupants for which an external source of the movement is not apparent. These vibrations, originating in irregularities of the rotating components, recur on subsequent rotations of the corners; and may be termed periodic. One particular type of periodic vibration involves torsional movement of the steering wheel and may be referred to as “smooth road shake.”